Tunable magnetron



April 14, 1953 F. H. cRAwFoRD ETAL 2,535,212

TUNABLE MAGNETRON Filed March 5, 1946 WAVELENGTH INVENTORS FRANZO H. CRAWFORD CARL G. HOK

Va/Wm 9, Mn

ATTORN EY sets of interleaving anode fingers.

Patented Apr. 14, 1953 TUNABLE MAGNETRON Franzo H. Crawford, Williamstown, Mass., and Carl G. Hok, Middletown, Conn, assignors to the United States of America the Secretary of War as represented. by .l.

'Application March 5, 1946, Serial No. 652,189 I This invention relates to electrical apparatus and mor particularly to improvements in tunable magnetrons.

One type of tunable magnetron radio frequency oscillator is the so called squirrel cage magnetron.

The "squirrel cage magnetron is generally constructed as a substantially cylindrical cavity Tresonator is a ring of interleaving anode fingers. ,Adja'cent fingers are connected at one end thereof to opposite annular anod halves, the opposite anode halves being connected. in turn to the opposite end closures of the cavity resonator.

Tuning of the magnetron is accomplished by relative axial movement of the interleaving anode fingers. In general, either one or both end closures are flexible and means are provided for moving the end closures with respect to on another. A magnetic field is maintained parallel to the magnetron axis in the usual fashion. The term squirrelcage is derived from the'appearance of the cylindrical ring formed by these two In one such magnetron described in the patent application of Franzo H. Crawford and Milton D. Hare, Serial No. 641,839, entitled Tunable Magnetron, filed January 17, 1946, issued on April 25, 1950 as Patent No. 2,505,529, means are described for increasing the tuning range of such magnetrons. However, in the devices described in the aforementioned "applicationwfCrawford et al., the capacity and the frequency-vary in a highly nonlinear H manner as the tuning adjustment is changed.

Accordingly, an object of the present invention is to produce a tunable squirrel cage magnetron wherein the tuning curve of frequency vs. motion of the tuningadjustment may be given any desired shape.

A further object of the present invention is to produce a tunable squirrel cage magnetron in which the tuning curve for the magnetron may be made substantially linear.

Other objects and advantages of the invention will be apparent during the course of the following description.

- In essence the present invention utilizes external capacity rings attached to one anode half and capacitively coupled to the anode fingers attached to the opposite anode half. By contouring the surfaces of these capacity rings which face the anode fingers (this contouring may be a circumferential contouring or less frequently 4 Claims. (01. 315- 40) a peripheral contouring), the. variations of capacity and consequently of frequency may be made to follow any desired form as the anode fingers and the overlapping'capacity rings are moved relative to one another.

In the accompanying drawing forming a of this specification:

Fig. 1 is a symbolic representation of the, con.- nections of the anode fingers and of'the'overlapping capacity fingers associated with said anode fingers, 3

Fig. 2 is a simplified cross sectional view taken on the line2-2 ofFig; 1', V

Fig. 3' is a cross sectional view taken on the same line as Fig. 2 of another embodiment in which the fingers are of a different shape than in Fig. 2,

Fig. 4 shows tuning curves for a magnetron such as described in the above-mentioned application of Crawford et al., Serial No. 641,839, curve A, and now Patent No. 2,505,529 for a magnetron embodying the principles of the present invention, curve B, and

Fig. 5 is a simplified isometric View, partly broken away, of a squirrel-cage magnetron of the type represented schematically in Figs. 1, 2,,and 3 except that the outer ring of anode fingers is omitted to avoid confusion. i

In Fig. 1, numerals l-l8 designate individual anode fingers which are arranged circumferentially about the axis of the magnetron to form .an interleaving squirrel cage anode structure. The blank anode fingers denote fingers attached to theupper annular anode half 29,- see Fig. 2, while the anode fingers having the Xmark de note fingers attached to the lower annular anode half 2|. Adjacent anode fingers are attached to opposite anode halves.

The arrangement of the anode fingers may be varied for reasons of efiiciency as may be under- ,stood by reference to the patent application of Franzo I-I. Crawford, Milton D. Hare and Carl G. Hok, Serial No. 652,186, entitled Magnetron, filed March 5, 1946, and to the application of Franzo H. Crawford and Carl G. Hok, Serial No. 652,187, entitled Tunable Magnetron, filed March 5, 1946. It is to be understood that the present invention is applicable to these modified forms as well, irrespective of the anode finger arrangement.

Radially overlapping, but spaced from, anode fingers l-IB is a ring of capacity fingers 3l48, each capacity finger being attached to the anode half opposite the anode half to which its corresponding anode finger is attached.

In Fig. 2, wherein is shown a simplified cross 7 part sectional view taken on the line 2-2 of Figl. the arrangement of the capacity fingers and anode fingers is mor clearly illustrated. Capacity finger 35 is electrically connected to and spaced from upper anode half 20 by means of the spacing ring 50 while capacity finger M is electrically connected to and spaced from lower anode half 21 by the spacing ring The anode halves 20 and 2| with their attached anode fingers and capacity fingers are constructed so as to be moveable axially with respect to one another in order to effect tuning of the magnetron. This construction may be similar to that described in the above-mentioned applica tion of the Crawford and Hare, ii desired.-

In Fig. 3 is shown an alternative shape of capacity fingers 35 and 44' which are contoured on the surfaces which face their respective anode fingers 5 and M respectively. The contour of this surface is optional and may be designed to secure any'desired tuning curve. As further regards the capacity fingers, they may be continuous cylindrical rings if desired. I These rings may further- .more, if desired, or if necessary, be slotted or notched to permit the interleaving thereof with "the opposite capacity ring. The contouring of the ring either in longitudinal cross section or in periphery may be modified to obtain any desired -tun-ing curve. 7

In Fig. 5 numeral 60 designates a cavity resonator, partly broken away to reveal the anode strucrturei Cavity resonator 60 may have any of the customary cavity resonator shapes, and in gen- ;.eral will be a figure of revolution circularly symmetrical about an axis (ll- EI. The cavity resosnator 60 has two opposing flexible diaphnagi'ndike walls or end closures 62 and 63.

Axially aligned along axis Sl -Bl are a filament 6d and cathode 65. A ring of interleaving anode posts or fingers 6'6 and '67 projecting from annular anode sections 58, 59 is concentrically arranged about cathodefifi and within cavity resonator 60. Alternate anode fingers 66 are connected to end closure 62 by being attached at one end to an annular anode section 58 and end plate .68 fixed to wall 62. The other anode fingers 61 are connected to the end closure 63 by being attached at oneend to another annular anode section 59 and end plate 69 fixed to wall '63. The magnetron may be tuned by flexing the walls 62 and 63 and thereby moving the anode sections 58, 59 together or apart to vary the capacity therebetween.

The radio rrequeney output or the magnetron 'may be taken ofi in the customary manner by any suitable coupling, not shown, to cavity reseiiator '60.

In Fig. 4 is shown the tuning" curve of waveiength vs. tuning adjustment for a magnetron su'c'nas described in the application Serial No. 641,839, curve A, as compared to that of a mag- '4 netron utilizing the principles of the present invention curve B. The tuning curve A is highly non-linear while tuning curve B is substantially linear over its central portion.

Many modifications of the embodiments of our invention disclosed herein will be apparent to those skilled in the art, and therefore these embodiments are only to be considered illustrative of our invention.

What is claimed is:

1 An anode structure for a tunable magnetron including two annular sections disposed coaxially and oppositeone another, a ring of interleaving anode fingers mounted circumferentially with a substantially uniform first given spacing about said axis, adjacent fingers being connected at one end thereof to opposite annular anode sections, a capacity ring of additional fingers mounted circumferentially with a substantially uniform second given spacing about said axis which is different from said first given spacing, said addito one anode section and being disposed in stag gered relationship relative to the anode fingers connected to said one anode section, whereby said additional fingers are capacitivelycoupled to the anode fingers connected to the other anode sec- ,tion, and means connected to said anode for mov'- ing said anode sections axially with respect to one 2. An anode structure according to claim 1, further including a second capacity ring of further additional fingers mounted circumferentially wane substantially uniform. second given spacirlg about said axis, said further additional fingers being connected at one end thereof to said other anode section and being disposed in staggered relationship relative to the anode fingers connected to said other anode section, whereby said further additional fingers are capacitively coupled to the anode fingers connected to said one anode section.

3. An anode structure according to claim wherein the shape of both said additional and further additional fingers is contoured to provide a particular tuning curve.

4. An anode structure according to claim 1, wherein the shape of said additional fingers is contoured to provide a particular tuning curve.

FRANZO' H. CRAWFORD. CARL G. HOK.

References Cited in the file 0f thiS patent UNITED STATES PATENTS Number Name Date 2,128,237 Dallenbach Aug. 30, 1933 2,144,222 Hollmann Jan. 117, 1939 2,409,222 Morton Oct. 15, 1946 2,424,886 Hansell July 29, 19d! 2,505,529 Crawford et a1. Apr. 25, 1950 

